[Tinycc-devel] tcc fails UBSan and ASan

[Giovanni Mascellani]

Hi,

the CodingStyle file suggests that tcc should be UBSan and ASan clean.
However, it appears it is not. Working with mob:

$ ./configure
$ make -j12
$ mv libtcc.a libtcc.a.hide
$ make clean
$ ./configure --extra-cflags="-fsanitize=undefined -g"
--extra-ldflags="-fsanitize=undefined -g"
$ make -j12

This already prints lots of errors when tcc compiles libtcc1.a, mostly
about unaligned struct access. An example:

> tcctools.c:189:21: runtime error: member access within misaligned address 
> 0x564f628c4d3c for type 'struct Elf64_Shdr', which requires 8 byte alignment
> 0x564f628c4d3c: note: pointer points here
>   00 00 00 00 01 00 00 00  01 00 00 00 06 00 00 00  00 00 00 00 00 00 00 00  
> 00 00 00 00 40 00 00 00
>               ^ 

Similar errors happen for other structs, like TokenString and TokenSym.

Then:

$ make test

Gives other similar errors, also for struct Sym. Also:

> tcctest.c: In function ‘switch_test’:
> tcctest.c:1969:6: error: case label does not reduce to an integer constant
>       case 4LL << 61:
>       ^~~~
> tcctest.c:1972:6: error: case label does not reduce to an integer constant
>       case 5LL << 61:
>       ^~~~

I'd say this is correct, this is undefined behaviour. Tests stop here
because of failure, but there could be more in later tests.

Let's do the same for ASan:

$ git clean -fdx
$ ./configure
$ make -j12
$ mv libtcc.a libtcc.a.hide
$ make clean
$ ./configure --extra-cflags="-fsanitize=address -g"
--extra-ldflags="-fsanitize=address -g"
$ make -j12
$ cp libtcc.a.hide libtcc.a
$ ./configure
$ make test

Some use-after-free are found in 07_function, 25_quicksort,
26_character_constants and 80_flexarray. Curiously, nothing is found in
VLA-related tests, while CodingStyle says there could be problems there.
More or less same results are obtained with valgrind.

I can try to fix them, but maybe people more knowledgable than me might
be quicker and produce a more correct fix.

Thanks, Giovanni.
-- 
Giovanni Mascellani <address@hidden>
Postdoc researcher - Université Libre de Bruxelles

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